Nanomodified backbones for polyimides with difunctional and mixed-functionality endcaps

ABSTRACT

Polyimides containing a backbone with at least one nanoparticle component and made from oligomers having endcaps that are difunctional or a mix of di- and monofunctionality are provided. The endcaps may be nadic or phenylethynyl. The backbone may be wholly inorganic or made from a mixture of inorganic and organic groups. The oligomers may be created in-situ using standard polymerization of monomeric reactants chemistry using a solvent or may be provided as a pre-imidized compound that may be either a solid or liquid. It is believed that the nanoparticle component of the polymer backbone provides superior thermo-oxidative stability verses unmodified organic backbones. It is further believed that providing difunctional or a mixture of di- and monofunctional endcaps allows for increased crosslinking to provide improved strength and stiffness verses wholly monofunctional endcapped oligomers for polyimides. The nanoparticle is part of the backbone of the polymer and not solely a pendant group.

FIELD

The implementations described herein generally relate to polyimideoligomers with nanomodified backbones and more particularly to polyimideoligomers having nanomodified backbones with functional endcaps, resinsystems including the polyimide oligomers with nanomodified backbones,composites formed therefrom and to their methods of use.

BACKGROUND

Only a few of the thermosetting resins that are commonly used today infiber-reinforced composites generally can be used in high-temperatureapplications (e.g., aerospace applications). These high-temperaturethermosetting resins are undesirable in many applications because theyoften form brittle composites that have relatively low thermalstabilities.

Recently, chemists have sought to synthesize oligomers forhigh-performance, high-temperature advanced composites suitable forhigh-temperature applications. These composites should exhibit solventresistance, be tough, impact resistant and strong, and be easy toprocess. Oligomers and composites that have thermo-oxidative stabilityare particularly desirable.

Imides and many other resin backbones have shown surprisingly highglass-transition temperatures, reasonable processing parameters anddesirable physical properties for high-performance, high-temperaturecomposites. However, typical polyimides are susceptible tothermo-oxidative aging that reduces their long-term strength andstiffness. Further, most formulations for high-temperaturepolymer-matrix composites have monofunctional endcaps which limit thedegree of crosslinking that can be attained.

Accordingly, there remains a need in the art for polyimide oligomershaving high thermo-oxidative stability with improved crosslinking andcomposites formed therefrom.

SUMMARY

The implementations described herein generally relate to polyimideoligomers with nanomodified backbones and more particularly to polyimideoligomers having nanomodified backbones with functional endcaps, resinsystems including the polyimide oligomers with nanomodified backbones,composites formed therefrom and to their methods of use.

According to one implementation described herein, a resin system isprovided. The resin system comprises a first capped oligomer having theformula:

Y_(i)-A-Y_(i),

wherein:

i=1 or 2;

Y is a nadic or a dinadic functional endcap; and

A is a chemical backbone, wherein the chemical backbone comprises one ormore nanoparticles. The resin system further comprises a second cappedoligomer having the formula:

D_(i)-Q-D_(i),

wherein:

i=1 or 2;

D is a nadic or a dinadic functional endcap; and

Q is a hydrocarbon backbone.

In another implementation described herein, a polyimide oligomer isprovided.

The polyimide oligomer has the formula:

Y_(i)-A-Y_(i),

wherein:

i=1 or 2;

Y is a nadic or dinadic functional endcap; and

A is a chemical backbone, wherein the chemical backbone comprises one ormore nanoparticles. The polyimide oligomer may be included in a resinsystem that further comprises at least one nadic or dinadic endcappedchemical backbone different from the chemical backbone A comprising thenanoparticle.

In another implementation, a polyimide oligomer comprising at least onenadic or dinadic amine functional endcap monomer and at least onechemical backbone, wherein the chemical backbone comprises one or morenanoparticles is provided.

In yet another implementation, a resin system is provided. The resinsystem comprises at least one nadic or dinadic endcapped chemicalbackbone, wherein the chemical backbone comprises a nanoparticle and atleast one nadic or dinadic endcapped chemical backbone different fromthe chemical backbone comprising the nanoparticle. The at least onenadic or dinadic endcapped nanoparticle comprising chemical backbone maycomprise at least one nadic or dinadic endcapped chemical backbone,wherein the chemical backbone has a nanoparticle incorporated in thechemical backbone and at least one nadic or dinadic endcappednanoparticle.

In yet another implementation, a resin system is provided. The resinsystem comprises the reaction product of one or more nanoparticlespossessing anhydride or amine functionality, at least one of nadic anddinadic endcap monomers possessing anhydride or amine functionality, andone or more oligomer backbones possessing anhydride or aminefunctionality such that the resin system may be reacted in-situ to formendcapped imide oligomers that may be subsequently reacted to formpolyimides.

In yet another implementation, a resin system is provided. The resinsystem comprises a first capped oligomer having the formula:

Y_(i)-A-Y_(i),

wherein:

i=1 or 2;

Y is a phenylethynyl or a diphenylethynyl functional endcap; and

A is a chemical backbone, wherein the chemical backbone comprises one ormore nanoparticles. The resin system further comprises a second cappedoligomer having the formula:

D_(i)-Q-D_(i),

wherein:

i=1 or 2;

D is a phenylethynyl or a diphenylethynyl functional endcap; and

Q is a hydrocarbon backbone.

In yet another implementation, a polyimide oligomer is provided. Thepolyimide oligomer has the formula:

Y_(i)-A-Y_(i),

wherein:

i=1 or 2;

Y is a diphenylethynyl functional endcap; and

A is a chemical backbone, wherein the chemical backbone comprises one ormore nanoparticles.

The features, functions, and advantages that have been discussed can beachieved independently in various implementations or may be combined inyet other implementations, further details of which can be seen withreference to the following description and drawings.

DETAILED DESCRIPTION

The following disclosure describes polyimide oligomers with nanomodifiedbackbones and more particularly to polyimide oligomers havingnanomodified backbones with functional endcaps, resin systems includingthe polyimide oligomers with nanomodified backbones, composites formedtherefrom and to their methods of use. Certain details are set forth inthe following description to provide a thorough understanding of variousimplementations of the disclosure. Other details describing well-knowndetails often associated with polyimide oligomers, resin systems, andcomposites formed therefrom are not set forth in the followingdisclosure to avoid unnecessarily obscuring the description of thevarious implementations.

Different aspects, implementations and features are defined in detailherein. Each aspect, implementation or feature so defined may becombined with any other aspect(s), implementation(s) or feature(s)(preferred, advantageous or otherwise) unless clearly indicated to thecontrary.

As used herein, the terms “substituent”, “radical”, “group”, “moiety”and “fragment” may be used interchangeably.

As used herein, the symbol “H” denotes a single hydrogen atom and may beused interchangeably with the symbol “—H”. “—H” may be attached, forexample, to an oxygen atom to form a “hydroxy” radical (i.e., —OH), ortwo “H” atoms may be attached to a carbon atom to form a “methylene”(—CH₂—) radical.

The terms “hydroxyl” and “hydroxy” may be used interchangeably.

If a substituent is described as being “optionally substituted,” thesubstituent may be either (1) not substituted or (2) substituted on asubstitutable position. If a substitutable position is not substituted,the default substituent is H.

Singular forms “a” and “an” may include plural reference unless thecontext clearly dictates otherwise.

The number of carbon atoms in a substituent can be indicated by theprefix “C_(A-B)” where A is the minimum and B is the maximum number ofcarbon atoms in the substituent.

As used herein, the term “halo” refers to fluoro (—F), chloro (—Cl),bromo (—Br) or iodo (—I).

As used herein, the term “alkyl” embraces a linear or branched acyclicalkyl radical containing from 1 to about 15 carbon atoms. In someimplementations, alkyl is a C₁₋₁₀ alkyl, C₁₋₆ alkyl or C₁₋₃alkylradical. Examples of alkyl include, but are not limited to, methyl,ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, sec-butyl,pentan-3-yl

and the like.

As used herein, “lower alkyl” refers to an alkyl group containing from 1to 6 carbon atoms, and may be straight chain or branched, as exemplifiedby methyl, ethyl, n-butyl, i-butyl, t-butyl. “Lower alkenyl” refers to alower alkyl group of 2 to 6 carbon atoms having at least onecarbon-carbon double bond.

As used herein, the term “alkynyl” refers to an unsaturated, acyclichydrocarbon radical with at least one triple bond. Such alkynyl radicalscontain from 2 to about 15 carbon atoms. Non-limiting examples ofalkynyl include ethynyl, propynyl and propargyl.

As used herein, the term “hydroxyalkyl” embraces alkyl substituted withone or more hydroxyl radicals. Hydroxyalkyl embraces, for example,monohydroxyalkyl, dihydroxyalkyl and trihydroxyalkyl. More specificexamples of hydroxyalkyl include hydroxymethyl, hydroxyethyl andhydroxypropyl (e.g., 2-hydroxypropan-2-yl).

As used herein, the term “haloalkyl” embraces alkyl substituted with oneor more halo radicals. Examples of haloalkyl include monohaloalkyl,dihaloalkyl and trihaloalkyl. A monohaloalkyl radical, for example, mayhave either a bromo, chloro, fluoro or iodo atom. A dihalo radical, forexample, may have two of the same halo radicals or a combination ofdifferent halo radicals. A trihaloalkyl radical may have three of thesame halo radicals or a combination of different halo radicals.Non-limiting examples of haloalkyl include fluoromethyl, difluoromethyl,trifluoromethyl (or CF₃), difluoroethyl, trifluoroethyl, difluoropropyl,tetrafluoroethyl, pentafluoroethyl, heptafluoropropyl, chloromethyl,dichloromethyl, trichloromethyl, dichloroethyl, trichloroethyl,dichloropropyl, tetrachloroethyl, pentachloroethyl, heptachloropropyl,dichlorofluoromethyl, difluorochloromethyl, bromomethyl, dibromomethyl,tribromomethyl, iodomethyl, diiodomethyl and triiodomethyl.

As used herein, the term “alkoxy” is RO— where R is alkyl. Non-limitingexamples of alkoxy include methoxy, ethoxy, propoxy and tert-butyloxy.The terms “alkyloxy”, “alkoxy” and “alkyl-O—” may be usedinterchangeably.

As used herein, the term “lower alkoxy” refers to alkoxy groups having1-6 carbon atoms in a straight or branched chain.

As used herein, the term “substituted aryl” and “substituted loweralkylaryl” and “substituted heteroaryl” and “substituted loweralkylheteroaryl” refer to aryl, heteroaryl, lower alkylaryl and loweralkylheteroaryl groups wherein the aryl and heteroaryl group may besubstituted with 1-3 substituents selected from lower alkyl, loweralkoxy, halogeno (i.e., chloro, fluoro, bromo and iodo), amino, carboxyand lower alkoxy carbonyl.

As used herein, the term “alkoxyalkyl” is ROR—, where R is alkyl.Examples of alkoxyalkyl radicals include methoxymethyl, methoxyethyl,methoxypropyl, ethoxyethyl and 2-methoxypropan-2-yl. The terms“alkoxyalkyl” and “alkyl-O-alkyl” may be used interchangeably.

As used herein, the term “amide” refers to a moiety containing the—CONH₂— group.

As used herein, the term “amideimide” refers to a moiety containing bothan amide and imide group as described herein.

As used herein, the term “amino” refers to NH₂, NHR, or NR₂ where R isan organic group.

As used herein, the term “aralkoxy” embraces arylalkyl attached to aparent molecular scaffold through an oxygen atom. The terms “arylalkoxy”and “aralkoxy” may be used interchangeably.

As used herein, the term “aryl” refers to any monocyclic, bicyclic ortricyclic cyclized carbon radical, wherein at least one ring isaromatic. An aromatic radical may be fused to a non-aromatic cycloalkylor heterocyclyl radical. Examples of aryl include phenyl and naphthyl.

As used herein, the term “aryloxy” is RO—, where R is aryl.

As used herein, the term “carbonyl” denotes a carbon radical having twoof four covalent bonds shared with a single oxygen atom

As used herein, the term “carboxy” embraces hydroxyl attached to one oftwo unshared bonds in a carbonyl radical

As used herein, the term “cyclic ring” embraces any aromatic ornon-aromatic cyclized carbon radical (e.g., aryl and cycloalkyl,respectively) which may contain one or more ring heteroatoms (e.g.,heterocyclyl and heteroaryl).

As used herein, the term “cycloalkyl” embraces any monocyclic, bicyclicor tricyclic cyclized carbon radical of 3 to about 15 carbon atoms thatis fully or partially saturated. Cycloalkyl may be fused, for example,to an aryl, cycloalkyl or a heterocyclyl radical. Cycloalkyl may besubstituted with, for example, alkyl, alkoxy, alkoxyalkyl, hydroxyl,hydroxyalkyl, amido, carboxy, acyl, carbamido, cyano, aminoalkyl,thiolalkyl, halo and/or haloalkyl.

As used herein, the term “ester” refers to the product of the reactionbetween a carboxylic acid and an alcohol

where R and R′ are the organic groups.

As used herein, the term “estersulfone” refers to a moiety containingboth an ester and a sulfone group as described herein.

As used herein, the term “ether” refers to a moiety containing thefunctional group RO—R′ where R and R′ are the organic groups.

As used herein, the term “etherimide” refers to a moiety containing bothan ether and an imide group as described herein.

As used herein, the term “ethersulfone” refers to a moiety containingboth an ether and a sulfone group as described herein.

As used herein, the term “heterocyclyl sulfone” refers to a moietycontaining both a heterocyclyl and a sulfone group as described herein.

As used herein, the term “heterocyclyl” refers to any monocyclic,bicyclic or tricyclic ring system having from 5 to about 15 ring membersselected from carbon, nitrogen, sulfur and oxygen, wherein at least onering member is a heteroatom. Heterocyclyl embraces a fully saturated,partially saturated and fully unsaturated radical (e.g., heteroaryl).Heterocyclyl may be fused to another heterocyclyl, aryl or cycloalkylradical.

Heterocyclyl embraces combinations of different heteroatoms within thesame cyclized ring system. When nitrogen is a ring member, heterocyclylmay be attached to the parent molecular scaffold through a ringnitrogen. Non-limiting examples of fully saturated five and six-memberedheterocyclyl include: pyrrolidinyl, imidazolidinyl, piperidinyl,piperazinyl, tetrahydrofuranyl, morpholinyl and thiazolidinyl. Examplesof partially saturated heterocyclyl include dihydrothiophenyl

dihydropyranyl, dihydrofuranyl and dihydrothiazolyl.

Heterocyclyl may be substituted with, for example, one or more alkyl,alkoxy, alkoxyalkyl, hydroxyl, hydroxyalkyl, amido, carboxy, acyl,carbamido, cyano, aminoalkyl, thiolalkyl, halo and haloalkyl radicals.Non-limiting examples of substituted heterocyclyl include 5- or6-membered heterocyclyl substituted with one or more alkyl, alkoxy,alkoxyalkyl, hydroxyl, hydroxyalkyl, amido, carboxy, acyl, carbamido,cyano, aminoalkyl, thiolalkyl, halo and haloalkyl radicals. Substitutedand un-substituted 5- and 6-membered heterocyclyl may be fused to anadditional heterocyclyl, aryl or cycloalkyl radical.

As used herein, the term “imide” refers to a functional group having twocarbonyl groups bridged through an amino group. The general formula ofan imide is:

where R, R′ and R″ are organic groups.

As used herein, the term “imidazole” refers to a moiety with the formulaC₃H₄N₂. This aromatic heterocyclic is classified as an alkaloid.

As used herein, the term “imidazolyl” refers to any of four monovalentradicals with the formula C₃H₃N₂ derived from imidazole by removal ofone hydrogen atom

As used herein, the term “imidesulfone” refers to a moiety containingboth an imide and a sulfone group as described herein.

As used herein, the term “imidazolyl sulfone” refers to a moietycontaining both an imidazolyl and a sulfone group as described herein.

As used herein, the term “moiety” is referred to throughout primarily asunivalent chemical moieties (e.g., alkyl, aryl, etc.). Nevertheless,such terms are also used to convey corresponding multivalent moietiesunder the appropriate structural circumstances clear to those skilled inthe art. For example, while an “alkyl” moiety generally refers to amonovalent radical (e.g., (CH₃—CH₂—), in certain circumstances abivalent linking moiety can be “alkyl,” in which case those skilled inthe art will understand the alkyl to be a divalent radical (e.g.,—CH₂—CH₂—), which is equivalent to the term “alkylene.” Similarly, incircumstances in which a divalent moiety is required and is stated asbeing “aryl,” those skilled in the art will understand that the term“aryl” refers to the corresponding multivalent moiety, arylene. Allatoms are understood to have their normal number of valences for bondformation (i.e., 1 for H, 4 for carbon, 3 for N, 2 for O, and 2, 4, or 6for S, depending on the oxidation state of the S).

As used herein, the term “oligomer” is a molecule possessing from about1 to 30 monomers. Specific oligomers that are used with theimplementations described herein include, for example, those having avariety of geometries such as linear, branched, or forked.

As used herein, the term “oxazole” refers to a five-member heterocyclehaving three carbon atoms, one oxygen atom, one nitrogen atom and twodouble bonds; the 1,3-isomer is aromatic.

As used herein, the term “oxazolyl” refers to a radical derived fromoxazole

As used herein, the term “oxazolyl sulfone” refers to a moietycontaining both an oxazolyl and a sulfone group as described herein.

As used herein, the term “sulfone” refers to a moiety containing asulfonyl functional group attached to two carbon atoms. The centralsulfur atom is twice double bonded to oxygen and has two further organicgroups. The general structural formula is R—S(═O)(═O)—R′ where R and R′are the organic groups.

As used herein, the term “thiazole” refers to any of a class ofunsaturated heterocyclic compounds or moieties containing a ring ofthree carbon atoms, a sulfur and a nitrogen atom; for example, C₃H₃SN.

As used herein, the term “thiazolyl” refers to a radical derived fromthiazole

As used herein, the term “thiazolyl sulfone” refers to a moietycontaining both a thiazolyl and a sulfone group as described herein.

Polyimides containing a backbone with at least one nanoparticlecomponent and made from oligomers having endcaps that aremonofunctional, difunctional or a mix of di- and monofunctional aredisclosed below in detail. Exemplary endcaps that may be used with theimplementations described herein include, for example, nadic, dinadic,phenylethynyl and diphenylethynyl endcaps. The backbone may be whollyinorganic or made from a mixture of inorganic and organic groups. Thebackbone may further include aromatic (e.g., phenyl) radicals betweenlinkages, although the backbone may have other aromatic, aliphatic, oraromatic and aliphatic radicals. The oligomers may be created in-situusing standard polymerization of monomeric reactant (PMR) chemistryusing a solvent or may be provided as a pre-imidized compound that maybe either a solid or liquid.

Inclusion of the nanoparticle component in the polymer backbone isbelieved to provide superior thermo-oxidative stability verses theunmodified organic backbones currently used in the art. Further,providing difunctional or a mixture of di- and monofunctional endcapsallows for increased crosslinking to provide improved strength andstiffness verses wholly monofunctional endcapped oligomers forpolyimides. The nanoparticles are present in the backbone and preferablyare not present as a pendant side group or in a pendant chain along thebackbone. In certain implementations, however, nanoparticles can beincorporated into the backbone and also incorporated into pendant sidechains from the backbone.

The polyimides with nanomodified backbones and the resin systemsdescribed herein are suitable for use in, among other things, thermosetcomposites.

Devising high-temperature composites that balance stiffness/strength andtoughness properties (impact strength) for different high-temperatureapplications is a challenge. Polyimide oligomers without stiff chainsegments tend to soften significantly with increasing temperature.Polyimide oligomers made with stiff backbones to improve their propertyretention with temperature generally are very difficult to processexcept at very high temperatures and, even in most cases, the ability toprocess may be very low. Incorporation of functionalized, stiff,nanoscale particles directly into the backbone of the polyimide oligomerused for producing composites should provide a balance of improvedstiffness and processability to provide the desired properties ofimproved toughness with minimal adverse effects on other compositeproperties. It is believed that only a small amount of functionalizednanoparticles is required to stiffen the polyimide oligomers asincorporation of such particles directly into the oligomer backboneshould increase stiffness above what would be expected from the rule ofmixtures because the stiffness is imparted directly, not through van derWaals interactions with the nanoparticles.

Polyimide oligomers for use in high-temperature polymer-matrixcomposites are disclosed below in detail. Polyimide oligomers accordingto the present disclosure provide composites with significantly improvedmechanical properties and increased thermo-oxidative stability.

Polyimide oligomers according to implementations of the presentdisclosure can have amine, anhydride, hydroxy, or acid chloridefunctionality to react with endcaps of various differentfunctionalities. For example, amine-functional backbones can react withanhydride-functional endcaps; acid chloride-functional backbones canreact with amine-functional endcaps; etc. Polyimide oligomers accordingto implementations of the present disclosure can be made from severalroutes, including, for example, starting with brominated compounds thatare reacted with phenylacetylene, using palladium-based catalysts, toreplace the bromines with phenylethynyl moieties.

Several commercially available nanoparticles can be incorporated into avariety of suitable oligomeric backbones for high-temperaturepolymer-matrix composites. Suitable nanoparticles include anynanoparticle capable of incorporation into the polyimide oligomerbackbone that provides improved thermo-oxidative stability. Thenanoparticle may be an organic nanoparticle. The nanoparticle may be aninorganic nanoparticle. The nanoparticle may be combination of bothorganic and inorganic components. By way of example, nanoparticles,suitable for use in the implementations of the present disclosure may bemade from any of the following, including, but not limited to, inorganicmaterial, for example, metal oxides, such as, but not limited to,silica, silicates, alumina, aluminum oxide, titanium oxide, orsemiconducting materials. The particles may also be composed of organicmaterial, such as semiconductor polymer particles, rubber particles, oranother organic material suitable for a particular application.

For the purposes of this disclosure, the term “nanoparticle” is used ina broad sense, though for illustrative purposes only, some typicalattributes of nanoparticles suitable for use in the implementationsdescribed herein are a particle size of between 1-100 nanometers andwith regards to particle shape, an aspect ratio of between 1 and 1,000.

The nanoparticles may be functionalized to introduce chemicalfunctionality to the nanoparticle. The nanoparticles may befunctionalized to with one or more functional groups such as, forexample, carboxy (e.g., carboxylic acid groups), epoxy, ether, ketone,amine, hydroxy, alkoxy, alkyl, aryl, aralkyl, alkaryl, lactone,functionalized polymeric or oligomeric groups, and the like, andcombinations thereof.

Exemplary nanoparticles that may be incorporated into the polyimideoligomer backbone include functionalized silsesquisiloxanes (e.g.,polyhedral oligomeric silsesquisiloxanes (POSS)), functionalized carbonblack, functionalized silicates, functionalized graphene, functionalizednanographite, functionalized carbon nanotubes, functionalized halloysitenanotubes, functionalized boron nitride nanotubes and combinationsthereof. Such compounds are merely provided as non-exhaustive exemplarylist of some (but not all) compounds suitable as building blocks forproviding polyimide oligomers having nanoparticles incorporated in itsbackbone.

Silsesquioxane nanoparticles, as disclosed herein, are a class ofinorganic-organic hybrid nanoparticles with reactive moieties.Silsesquioxane nanoparticles, also referred to as polysilsesquioxanes,polyorganosilsesquioxanes, or polyhedral oligomeric silsesquioxane(POSS) nanoparticles, are polyorganosilicon oxide compounds having thegeneral formula RSiO_(1.5) (where R is a hydrogen, inorganic group, ororganic group such as methyl) having defined closed or open cagestructures with chemically specific organic peripheral groups. Theorganic peripheral groups are covalently bonded to each silicon atom,which provides POSS molecules with specific interactions to othermolecules in the medium.

Silsesquioxane nanoparticles can be prepared by acid and/orbase-catalyzed condensation of functionalized silicon-containingmonomers such as tetraalkoxysilanes including tetramethoxysilane andtetraethoxysilane, alkyltrialkoxysilanes such as methyltrimethoxysilaneand methyltrimethoxysilane.

Silsesquioxane nanoparticles can have any shape of cage structure suchas cubes, hexagonal prisms, octagonal prisms, decagonal prisms,dodecagonal prisms, and the like. Additionally, the cage structure ofthe silsesquioxane nanoparticles comprises from 4 to 30 silicon atoms(e.g., from 4 to 20 silicon atoms; from 4 to 16 silicon atoms), witheach silicon atom in the cage structure being bonded to oxygen. Itshould be noted that the term “cage structure” is meant to include theSiO_(1.5) portion of the general silsesquioxane formula RSiO_(1.5), andnot the R-group.

Exemplary silsesquioxane nanoparticles usable herein include, but arenot limited to, POSS molecules represented by the chemical formula(SiO_(1.5))_(n)R_(n-1)R′, wherein n=6, 8, 10, 12, R is alkyl having 1 to6 carbon atoms or phenyl, R′ is —R—B; R₁ is alkyl having 1 to 6 carbonatoms or phenyl, and B is selected from group at least consisting —NH₂,—OH, —Cl, —Br, —I, or other derivatives having a diamine group (2NH₂),for example, a reactive functional groups as —R₁—N(—Ar—NH₂)₂,—R₁—O—Ar—CH(—Ar—CH(—Ar—NH₂)₂, and the like.

Carbon black (CB) nanoparticles, as disclosed herein, includeparticulate carbon formed by the pyrolysis/incomplete combustion ofheavy petroleum products. Carbon black is primarily an amorphous form ofcarbon having a greater or lesser concentration of graphitic phasedistributed throughout the pigment. Carbon black is typically composedof domains of aromatic rings or small graphene sheets, wherein aromaticrings or graphene sheets in adjoining domains are connected throughchemical bonds in the disordered phase (matrix).

Silicate nanoparticles, also referred to as silica nanoparticles, ornanosilica are SiO₂ particles.

Graphene and nanographene, as disclosed herein, are effectivelytwo-dimensional particles having one or more layers of fused hexagonalrings with an extended delocalized π-electron system, layered and weaklybonded to one another. Graphene in general, including nanographene, canbe a single sheet or a stack of several sheets having both micro- andnano-scale dimensions, such as in some implementations an averageparticle size of 1 to 20 micrometers (e.g., 1 to 15 micrometers), and anaverage thickness (smallest) dimension in nano-scale dimensions of lessthan or equal to 50 nm (e.g., less than or equal to 25 nm; less than orequal to 10 nm). An exemplary nanographene can have an average particlesize of 1 to 5 micrometers (e.g., 2 to 4 micrometers).

Graphene can be prepared by exfoliation of graphite or by a syntheticprocedure by “unzipping” a nanotube to form a nanographene ribbon,followed by derivatization of the nanographene to prepare, for example,graphene oxide.

Nanographite is a cluster of plate-like sheets of graphite, in which astacked structure of one or more layers of graphite, which has aplate-like two dimensional structure of fused hexagonal rings with anextended delocalized π-electron system, are layered and weakly bonded toone another through n-n stacking interaction. Nanographite has a layeredstructure of greater than or equal to about 50 single sheet layers(e.g., greater than or equal to about 100 single sheet layers; greaterthan or equal to about 500 single sheet layers). Nanographite has bothmicro- and nano-scale dimensions, such as for example art averageparticle size of 1 to 20 micrometers (e.g., 1 to 15 micrometers), and anaverage thickness (smallest) dimension in nano-scale dimensions, and anaverage thickness of less than 1 micrometer (e.g. less than or equal to700 nm; less than or equal to 500 nm).

Nanotubes include carbon nanotubes, inorganic nanotubes such as boronnitride nanotubes, metallated nanotubes, or a combination comprising atleast one of the foregoing. Nanotubes are tubular structures having openor closed ends and which are inorganic (e.g. boron nitride) or madeentirely or partially of carbon. In one implementation, carbon andinorganic nanotubes include additional components such as metals ormetalloids, which are incorporated into the structure of the nanotube,included as a dopant, form a surface coating, or a combinationcomprising at least one of the foregoing. Nanotubes, including carbonnanotubes and inorganic nanotubes, are single walled nanotubes (SWNTs)or multi-walled nanotubes (MWNTs).

Carbon nanotubes and nanofibers are graphitic nanofilaments withdiameters ranging from about 0.4 nanometers to about 500 nanometers andlengths which typically range from a few micrometers to a fewmillimeters. Graphitic nanofilaments may be categorized according to atleast four distinct structural types, namely, tubular, herringbone,platelet, and ribbon. The term “nanotube” may be used to describe thetubular structure whereas “nanofiber” may describe the non-tubularforms.

Carbon nanotubes are generally classified as single-walled carbonnanotubes and multi-walled carbon nanotubes. The SWNT is a graphiticnanofilament which comprises a cylindrical carbon molecule that may beconceptualized as a one-atom thick sheet of graphite called graphenerolled into a seamless graphene tube. The graphene tube forms acylindrical wall which is parallel to the filament axis direction. Oneor more of the nanotube ends may be capped by additional carbon atoms.

Halloysite is a material represented by AlSi₂O₅(OH)₄.2H₂O and is analuminum silicate clay mineral having a ratio of aluminum to silicon of1:1. The halloysite is a nano-sized plate type and has a layer structurein which different layers are alternately layered in a ratio of 1:1.Moreover, the halloysite is naturally present in aluminosilicate. Theouter surface of the halloysite typically comprises a silicate SiO₂ ⁻layer, and the inner surface comprises an alumina Al₂O₃ ⁺ layer. Thehalloysite has a hollow nanotubular structure. In some implementations,the inner diameter of the halloysite nanotube is about 30 to 250 nm andthe length is about 200 to 400 nanometers.

In one exemplary implementation, a resin system including polyimideoligomers having chemical backbones incorporating nanoparticles isprovided for tailoring the mechanical properties of composites formedfrom the resin system while retaining ease of processing. The resinsystem can be a mixture of at least one of the following to achievedesired properties: (1) chemical backbones incorporating nanoparticles;(2) chemical backbones that are nanoparticles; (3) chemical backbonesthat do not incorporate nanoparticles; (4) difunctional endcaps; and (5)monofunctional endcaps. The chemical backbones may be the same. Thechemical backbones may be different. The resin system typicallycomprises at least one monofunctionally or difunctionally endcappedchemical backbone, wherein the chemical backbone comprises ananoparticle and at least one monofunctionally or difunctionallyendcapped chemical backbone different from the chemical backbonecomprising the nanoparticle. The at least one monofunctionally ordifunctionally endcapped nanoparticle comprising chemical backbone maycomprise at least one monofunctionally or difunctionally endcappedchemical backbone, wherein the chemical backbone has a nanoparticleincorporated in the chemical backbone and at least one monofunctionallyor difunctionally endcapped nanoparticle.

In some implementations, the resin system may be a pre-imidized mixtureof monofunctionally and/or difunctionally endcapped chemical backbones.The chemical backbones may all possess the same endcap chemistry.Pre-imidization of the oligomers typically avoids condensation reactionsduring chain extension. In some implementations, the resin system may bea mixture of components (e.g., monofunctional and/or difunctionalendcaps, chemical backbones and functionalized nanoparticles) which arereacted in-situ to form endcapped chemical backbones in the resinsystem. The endcapped chemical backbones may be formed in-situ via, forexample, PMR chemistry.

The ratio of components may be varied to achieve the desired mixture ofprocessability and mechanical properties (e.g., stiffness andtoughness). In some implementations, the ratio of difunctional endcapsto monofunctional endcaps may be varied. The resin system may includefrom about 0% to about 99% of the chemical backbones havingmonofunctional endcaps and from about 1% to about 100% of the chemicalbackbones having difunctional endcaps. The resin system may include fromabout 0% to about 75% of the chemical backbones having monofunctionalendcaps and from about 25% to about 100% of the chemical backboneshaving difunctional endcaps. The resin system may include from about 1%to about 50% of the chemical backbones having monofunctional endcaps andfrom about 50% to about 99% of the chemical backbones havingdifunctional endcaps. The resin system may include from about 1% toabout 25% of the chemical backbones having monofunctional endcaps andfrom about 75% to about 99% of the chemical backbones havingdifunctional endcaps.

In some implementations, the ratio of chemical backbones incorporatingnanoparticles to chemical backbones without nanoparticles may be varied.The resin system may include from about 0% to about 99% of chemicalbackbones without nanoparticles and from about 1% to about 100% of thechemical backbones incorporating nanoparticles. The resin system mayinclude from about 0% to about 75% of chemical backbones withoutnanoparticles and from about 25% to about 100% of the chemical backbonesincorporating nanoparticles. The resin system may include from about 1%to about 50% of the chemical backbones without nanoparticles and fromabout 50% to about 99% of the chemical backbones incorporatingnanoparticles. The resin system may include from about 1% to about 25%of the chemical backbones without nanoparticles and from about 75% toabout 99% of the chemical backbones incorporating nanoparticles.

The chemical backbones of the monofunctional and difunctional endcappedgroups may be different in order to confer improved processability ormechanical properties. As described herein, the chemical backbonespresent in the resin system may be independently selected from organicbackbones, organic backbones incorporating nanoparticles, andnanoparticles bonded directly to the endcaps. The chemical backbones maybe from different chemical families.

The resin system allows tailoring of the properties of high-performancecomposites. The resin system allows averaging of the properties ofdifferent polyimide oligomers to provide composites that do not have assevere shortcomings as the pure compounds. For example, the rigid natureof a resin system incorporating all difunctionally endcapped oligomerscan be reduced by a resin system comprising a mixture of difunctionallyand monofunctionally endcapped backbones. The resulting resin systemwill produce composites having improved stiffness relative to compositesproduced from a resin system having all monofunctionally endcappedoligomers and flexibility greater than composites produced from a resinsystem having all difunctionally endcapped oligomers. Accordingly, theresulting composites have a blending or averaging of physicalproperties, which makes them candidates for particularly harshconditions.

While not wishing to be bound by theory, it is believed that theinclusion or exclusion of nanoparticles from the chemical backbones ofthe resin system allows further tailoring of the properties ofhigh-performance composites. For example, the rigid nature of a resinsystem including all chemical backbones incorporating nanoparticles maybe reduced by a resin system comprising a mixture of chemical backbonesincorporating nanoparticles and chemical backbones withoutnanoparticles. It is also believed that the resulting resin system willproduce composites having a use temperature (thermo-oxidative stability)higher than composites produced from a resin system having all chemicalbackbones without nanoparticles and flexibility greater than compositesproduced from a resin system having all chemical backbones incorporatingnanoparticles. Accordingly, it is believed that the resulting compositeshave a blending or averaging of physical properties, which makes themcandidates for particularly harsh conditions.

In one implementation, a polyimide oligomer having one or morenanoparticles incorporated into an oligomer backbone to increasethermo-oxidative stability is provided. In one implementation, thepolyimide oligomer has the following formula:

Y_(i)-A-Y_(i);

wherein:

i=1 or 2; and

A is a chemical backbone comprising one or more nanoparticles. The oneor more nanoparticles may be incorporated in the chemical backbone. Theone or more nanoparticles may be the chemical backbone. It is believedthat incorporation of one of more nanoparticles into the backboneincreases thermo-oxidative stability of the polyimide oligomer. In someimplementations, the chemical backbone A may further include aromatic(e.g., phenyl) radicals between linkages, although they may have otheraromatic, aliphatic, or aromatic and aliphatic radicals.

Y may be an endcap having the desired crosslinking functionality. Y maybe any endcap having at least one crosslinking functionality such as amono-functional endcap. Y may be any endcap having two or morecrosslinking functionalities such as a multi-functional or di-functionalendcap. Y may be selected from mono-functional endcaps and di-functionalendcaps. Exemplary endcaps that may be used with the implementationsdescribed herein include nadic endcaps, dinadic endcaps, phenylethynylendcaps and diphenylethynyl endcaps. Exemplary phenylethynyl endcaps anddiphenylethynyl endcaps that may be used with the implementationsdescribed herein are described in U.S. Pat. No. 5,817,744 titledPhenylethynyl Capped Imides to Shepard et al. and U.S. Pat. No.8,106,142 titled Polyacetylinic Oligomers to Tsotsis et al. both ofwhich are incorporated by reference in their entirety. Exemplary nadicand dinadic endcaps that may be used with the implementations describedherein are described in U.S. Patent Application Publication No.2008/0300374 titled Dinadic Phenyl Amine Reactive Endcaps to Lubowitz etal.

In one implementation, Y is derived from a nadic phenyl amine endcapmonomer for application in high temperature polymeric composites.Exemplary nadic phenyl amine endcap monomers may be selected from thefollowing formulae:

In one implementation, Y is derived from a dinadic phenyl amine endcapmonomer for application in high temperature polymeric composites.Exemplary dinadic phenyl amine endcap monomers may be selected from thefollowing formulae:

(NA) is nadic anhydride illustrated by the formula:

wherein:

G=—CH₂—, —SO₂—, —S—, —O—, or —CO—, and

R=hydrogen, lower alkyl (e.g., saturated or unsaturated, linear orbranched), phenyl, lower alkoxy, aryl, aryloxy, substituted aryl,substituted alkyl, or mixtures thereof.

Amines can be obtained by numerous methods known in the art includingdirect amination, arylation or alkylation of ammonia or amines and freeradical addition of amines to olefins. Implementations of the dinadicphenyl amine reactive endcaps of the present disclosure can be readilysynthesized by first converting 3,5-diamino benzoic acid to a dinadiccarboxylic acid as follows:

In one implementation, the dinadic carboxylic acid is reacted withsodium azide to form a cyanate, which is then converted to an amine byhydrolysis via a Curtius rearrangement as illustrated below:

Alternatively, the dinadic carboxylic acid may be reacted with an azideunder acidic conditions to form an acyl azide, which rearranges to anisocyanate. The isocyanate is hydrolyzed to carbamic acid anddecarboxylated to form the amine as illustrated below:

In one alternative implementation, dinadic phenyl amine reactive endcapsare synthesized by first converting 2,4-diamino phenol to form a dinadicphenol as follows:

The dinadic phenol can be converted to a dinadic phenyl amine byutilizing either a Curtius rearrangement or a Schmidt reaction.Exemplary synthesis methods of the dinadic phenyl amine reactive endcapsof the present disclosure are further described in United States PatentApplication Publication No. 2008/0300374, titled DINADIC PHENYL AMINEREACTIVE ENDCAPS, which is incorporated by reference herein in itsentirety.

In one implementation, Y is derived from a phenylethynyl endcap monomerfor application in high temperature polymeric composites. Exemplaryphenylethynyl endcap monomers may be selected from the followingformulae:

wherein R=hydrogen, lower alkyl, or phenyl.

In one implementation, Y is derived from a diphenylethynyl endcapmonomer for application in high temperature polymeric composites.Exemplary diphenylethynyl endcap monomers may be selected from thefollowing formulae:

or

whereinPh=phenyl;

G=—SO₂—, —S—, —O—, —CH₂—, —CO—, —SO—, —CHR—, —CR₂—, C₃F₆, or NHCO; and

R₁=amine, hydroxyl, acid chloride, or anhydride, where R₁ is the pointof attachment to the oligomeric backbone. In one implementation,

-   -   R₁=

wherein R₂=hydrogen, lower alkyl (e.g., saturated or unsaturated, linearor branched), phenyl, lower alkoxy, aryl, aryloxy, substituted aryl,substituted alkyl, or mixtures thereof.

Diphenylethynyl endcap monomers cart be obtained by numerous methodsknown in the art including by starting with brominated compounds, whichare reacted with phenyl acetylene using palladium-based catalysts toreplace the bromines with phenylethynyls. For example, thediphenylethynyl endcap monomers can be prepared by the followingreaction scheme:

R=

R′=alkyl, aryl, e.g. CH₃, and phenyl; and

G=—SO₂—, —S—, —O—, —CH₂—, —CO—, —SO—, C₃F₆, or NHCO.

The bromine compounds are then reacted with a phenylethynyl acetyleneusing a palladium catalyst:

whereinPh=phenylR₁=amine, hydroxyl, acid chloride, or anhydride.

In another implementation, the following reaction scheme can be used.

Suitable palladium catalyst to be used for displacement of a halogenatom from an organic moiety with an acetylinic moiety, include, but arenot limited to: Pd/(PPh₃)₂; PdCl₂/(PPh₃)₂; PdCl₂/CuCl₂/LiCl;Pd(OAc)₂/PPh₃/Et₃N; Pd/(PPh₃)₄. Also, palladium-on-carbon (5% Pd/C);(30% Pd/C) or palladium black (pure Pd) can be used. Additionally, PdOor Pd(OAc)₂/benzimidazolium salts can be used. In an exemplaryimplementation, the palladium catalyst, for example, Pd/(PPh₃)₂ orPdCl₂/(PPh₃)₂, is used in the presence of a base, for example,triethyethylamine, a Cu(I) salt, and a solvent, for example, a polarsolvent, for example, tetrahydrofuran.

The acetylene arylation reaction is run in an inert atmosphere atatmospheric pressure at a temperature of 65-85° C. for varying lengthsof time, ranging from 6-48 hours, depending on the particular arylbromide used in the reaction. The time and temperature required isdependent on the nature and position of other substituents on thearomatic nucleus of the aryl bromide.

Other useful amines which can be used in place of triethylamine include,for example, diethylamine, butylamines, pyridine and the like.

A co-solvent such as toluene, xylene, dimethylformamide, ordimethylacetamide can also be used to improve the solubility of thereactants and/or product. The reaction requires the presence of ahomogenous palladium catalyst which, for example, can bebis(triphenylphosphine)palladium (II) chloride ortetrakis(triphenylphosphine)palladium (O). To improve the utility of thepalladium catalyst, an excess of the phosphine ligand is used. Examplesof such phosphine ligands include: triorthotoluylphosphine andtriphenylphosphine which is preferred because of its availability andcost. The use of palladium complexes to catalyze reactions of this typeis described in the literature, for example, F. R. Heck and H. A. Dieck,J. Organometallic Chem., 93, p. 259-263 (1975). To further facilitatethe reaction a co-catalyst may also be used.

Suitable co-catalysts include cuprous salts, for example, cuprouschloride, cuprous bromide, and cuprous iodide. The reaction is monitoredby gas or thin-layer chromatography, monitoring the disappearance ofreactants and/or appearance of product.

Exemplary synthesis methods of the diphenylethynyl endcap monomers ofthe present disclosure are further described in U.S. Pat. No. 8,106,142,titled POLYACETYLINIC OLIGOMERS, which is incorporated by referenceherein in its entirety.

Chemical backbone A in formula Y_(i)-A-Y_(i) is typically a chemicalbackbone comprising one or more nanoparticles. The one or morenanoparticles may be incorporated in the chemical backbone. The one ormore nanoparticles may be the chemical backbone A. The chemical backboneA may be composed of all organic components. The chemical backbone A maybe composed of all inorganic components. The chemical backbone A may becomposed of a mixture of inorganic and organic components.

The chemical backbone A may be an aromatic, aliphatic, oraromatic/aliphatic hydrocarbon backbone incorporating the one or morenanoparticles. The chemical backbone A may be a backbone incorporatingthe one or more nanoparticles. The chemical backbone A may furtherinclude moieties selected from the group consisting of: imidesulfone,ether, ethersulfone, amide, imide, ester, estersulfone, etherimide,amideimide, oxazolyl, oxazolyl sulfone, thiazolyl, thiazolyl sulfone,imidazolyl, imidazolyl sulfone, heterocyclyl sulfone and combinationsthereof. In some implementations, the chemical backbone A may furtherinclude aromatic (e.g., phenyl) radicals between linkages, although theymay have other aromatic, aliphatic, or aromatic and aliphatic radicals.Without being bound by theory, it is believed that inclusion of the atleast one nanoparticle into the chemical backbone A leads tocrosslinking not only at the endcaps but also at the nanoparticle withinthe backbone of the oligomer itself.

Nanoparticles, from which the derivatized nanoparticles are formed, aregenerally particles having an average particle size in at least onedimension, of less than one micrometer (in). As used herein “averageparticle size” refers to the number average particle size based on thelargest linear dimension of the particle (sometimes referred to as“diameter”). Particle size, including average, maximum, and minimumparticle sizes, may be determined by an appropriate method of sizingparticles such as, for example, static or dynamic light scattering (SLSor DLS) using a laser light source. Nanoparticles may include bothparticles having an average particle size of 250 nm or less, andparticles having an average particle size of greater than 250 nm to lessthan 1 μm (sometimes referred to in the art as “sub-micron sized”particles). In one implementation, a nanoparticle may have an averageparticle size of about 0.01 to about 500 nanometers (nm), specifically0.05 to 250 nm, more specifically about 0.1 to about 150 nm, morespecifically about 0.5 to about 125 nm, and still more specificallyabout 1 to about 75 nm. The nanoparticles may be monodisperse, where allparticles are of the same size with little variation, or polydisperse,where the particles have a range of sizes and are averaged.Nanoparticles of different average particle size may be used, and inthis way, the particle size distribution of the nanoparticles may beunimodal (exhibiting a single distribution), bimodal exhibiting twodistributions, or multi-modal, exhibiting more than one particle sizedistribution.

The nanoparticle may be any nanoparticle capable of incorporation intothe polyimide oligomer backbone that provides improved thermo-oxidativestability. The nanoparticle may be an organic nanoparticle. Thenanoparticle may be an inorganic nanoparticle. The nanoparticle may be acombination of both organic and inorganic components. Exemplarynanoparticles that may be incorporated into the polyimide oligomerbackbone include functionalized silsesquisiloxanes (e.g., polyhedraloligomeric silsesquisiloxanes (POSS)), functionalized carbon black,functionalized silicates, functionalized graphene (e.g., nanographene),functionalized nanographite, functionalized carbon nanotubes (e.g.,single- or multiwalled nanotubes), functionalized halloysite nanotubes,functionalized boron nitride nanotubes and combinations thereof.

The nanoparticles used herein are typically derivatized to include oneor more functional groups such as, for example, carboxy (e.g.,carboxylic acid groups), epoxy, ether, ketone, amine, hydroxy, alkoxy,alkyl, aryl, aralkyl, alkaryl, lactone, functionalized polymeric oroligomeric groups, and the like, and combinations thereof. Thenanoparticles are derivatized to introduce chemical functionality to thenanoparticle. For example, for carbon nanotubes, the surface and/oredges of the carbon nanotubes may be derivatized to increase stiffnessof the polyimide oligomer.

In one implementation, the nanoparticle is derivatized by, for example,amination to include amine groups, where amination may be accomplishedby nitration followed by reduction, or by nucleophilic substitution of aleaving group by an amine, substituted amine, or protected amine,followed by deprotection as necessary. In another implementation, thenanoparticle can be derivatized by oxidative methods to produce anepoxy, hydroxy group or glycol group using peroxide, or by cleavage of adouble bond by for example a metal-mediated oxidation such as apermanganate oxidation to form ketone, aldehyde, or carboxylic acidfunctional groups.

In another implementation, the nanoparticle can be further derivatizedby grafting certain polymer chains to the functional groups. Forexample, polymer chains such as acrylic chains having carboxylic acidfunctional groups, hydroxy functional groups, and/or amine functionalgroups; polyamines such as polyethyleneamine or polyethyleneimine; andpoly(alkylene glycols) such as poly(ethylene glycol) and poly(propyleneglycol), may be included by reaction with functional groups.

The functional groups of the derivatized nanoparticles may be selectedsuch that the derivatized nanoparticles will be incorporated into thebackbone of the polyimide oligomer to impart improved properties such ashigher stiffness.

The exemplary sequence below illustrates the functionalization of anexemplary silicate nanoparticle (e.g., an amine-functionalized silica,nanoparticle).

The amine-functionalized silica nanoparticle may be prepared as follows:0.05 mol of (3-aminopropyl)trimethoxysilane and 0.2 mole of tetraethylorthosilicate may be reacted in the presence of 2-propanol and nonionicsurfactant for 4 hours at 25 degrees Celsius. The precipitate may befiltered, washed with deionized water and dried.

The nanoparticles can also be blended in with other, more common fillerparticles such as carbon black, mica, clays such as e.g.,montmorillonite clays, silicates, glass fiber, carbon fiber, and thelike, and combinations thereof.

In one implementation, the nanoparticles are present in the amount ofabout 0.001 to about 10 wt, % based on the total weight of the resinsystem. In another implementation, the nanoparticles are present in theamount of about 0.01 to about 5 wt. % based on the total weight of theresin system. In yet another implementation, the nanoparticles arepresent in the amount of about 0.01 to about 1 wt. % based on the totalweight of the resin system.

One exemplary sequence illustrating the incorporation of a nanoparticle(e.g., carbon black) into a polyimide oligomer is disclosed inFabrication of Polyimide Composite Films Based On Carbon Black ForHigh-Temperature Resistance, Kwon, et al., Polymer Composites 2010 43(22), 9337-9347.

In another implementation, an endcapped nanoparticle is provided. Theendcapped nanoparticle may have the following formula:

Z_(i)—B—Z_(i)

wherein:

i=1 or 2;

Z is an endcap including at least one crosslinking functionality; and

B is a nanoparticle which serves as the backbone for the endcap Z. It isbelieved that using a nanoparticle as the backbone increases themechanical performance and/or thermo-oxidative stability of thepolyimide oligomer. In some implementations, the chemical backbone B mayfurther include aromatic (e.g., phenyl) radicals between linkages,although they may have other aromatic, aliphatic, or aromatic andaliphatic radicals.

Z may be any endcap including the desired crosslinking functionality. Zmay be any endcap including at least one crosslinking functionality suchas a mono-functional endcap. Z may be any endcap including two or morecrosslinking functionalities such as a multi-functional or di-functionalendcap. Exemplary endcaps include nadic endcaps, dinadic endcaps,phenylethynyl endcaps and diphenylethynyl endcaps as previouslydescribed herein.

The nanoparticle B may be any nanoparticle that provides improvedthermo-oxidative stability and is capable of functioning as a backbonefor the endcap Z. The nanoparticle B may be any of the nanoparticlespreviously described herein.

In one implementation, B is POSS and Z is (phenylethynylphthalimide)PEPA. Exemplary POSS with a PEPA moiety that may be used with theimplementations described herein are disclosed in Thermal Transitionsand Reaction Kinetics of Polyhederal Silsesquioxane containingPhenylethynylphthalimides, Seurer, Vij, Haddad, Mabry, and Lee,Macromolecules 2010 43 (22), 9337-9347. One known reaction scheme forformation of POSS with a PEPA moiety as disclosed in Seurer et al. isillustrated as follows:

In another implementation, a polyimide oligomer having an oligomerbackbone is provided. The polyimide oligomer having an oligomer backbonemay be combined with any of the aforementioned polyimide oligomershaving nanoparticles incorporated therein. In one implementation, thepolyimide oligomer having an oligomer backbone has the followingformula:

D_(i)-Q-D_(i)

wherein:

i=1 or 2;

D is an endcap including at least one crosslinking functionality; and

Q is an aromatic, aliphatic, or aromatic/aliphatic hydrocarbon backbone.In some implementations, the backbone (Q) is selected from the groupconsisting of imidesulfone; ether; ethersulfone; amide; imide; ester;estersulfone; etherimide; amideimide; oxazole; oxazole sulfone;thiazole; thiazole sulfone; imidazole; and imidazole sulfone. Thebackbone (Q) does not contain a nanoparticle. In some implementations,the chemical backbone Q may further include aromatic (e.g., phenyl)radicals between linkages, although they may have other aromatic,aliphatic, or aromatic and aliphatic radicals. Exemplary backbones aredescribed in U.S. Pat. No. 5,817,744 titled Phenylethynyl Capped Imidesto Shepard et al., U.S. Pat. No. 8,106,142 titled PolyacetylinicOligomers to Tsotsis et al., and U.S. Patent Application Publication No.2008/0300374 titled Dinadic Phenyl Amine Reactive Endcaps to Lubowitz etal. all of which rare incorporated by reference in their entirety.

In some implementations, D_(i)-Q-D_(i) comprises the reaction product ofat least one of the aforementioned endcap monomers and a chemicalbackbone according to the formula:

wherein R is selected from the group consisting of:

wherein L is —CH₂—, —(CH₃)₂C—, —S—, —SO₂— or —CO—; andwherein y is —S—, —SO₂— or —(CF₃)₂C—, —O—, —(CH₃)₂C—; and in certainimplementations, n is selected such that the molecular weight does notexceed about 3000.

In another implementation, polyimide oligomers of the present disclosurecomprise the reaction product of at least one of the aforementionedendcap monomers and a chemical backbone according to the formula:

wherein R is selected from the group consisting of:

wherein L is —CH₂—, —(CH₃)₂C—, —S—, —SO₂— or —CO— andwherein y is —S—, —SO₂— or —(CF₃)₂C—, —O—, —(CH₃)₂C—; and in certainimplementations, n is selected such that the molecular weight does notexceed about 3000.

In addition to the traditional schemes for synthesizing polyimideoligomers, various polyimide oligomer implementations of the of thepresent disclosure can be formed by directly reacting at least one ofthe aforementioned endcaps with any chemical backbone that is capable ofreacting with an amine and is suitable for high-temperature composites.In various implementations, at least one of the aforementioned endcapsis directly reacted with a precursor capped with acid anhydrides to forman oligomer which is suitable for high-temperature composites. Thedirect reaction between a dinadic amine endcap and an acidanhydride-capped precursor forms a tetrafunctional oligomer appropriatefor high-temperature composites. Accordingly, implementations of thepresent disclosure provide a method of synthesizing an endcappedoligomer suitable for high-temperature compositions whereby costlyintermediate steps are eliminated.

D may be any endcap including the desired crosslinking functionality. Dmay be any endcap including at least one crosslinking functionality suchas a monofunctional endcap. D may be any endcap including two or morecrosslinking functionalities such as a multifunctional or difunctionalendcap. Exemplary endcaps include nadic endcaps, dinadic endcaps,phenylethynyl endcaps and diphenylethynyl endcaps including the endcapspreviously described herein. Exemplary phenylethynyl endcaps anddiphenylethynyl endcaps are described in U.S. Pat. No. 5,817,744 titledPhenylethynyl Capped Imides to Shepard et al. and U.S. Pat. No.8,106,142 titled Polyacetylinic Oligomers to Tsotsis et al. both ofwhich are incorporated by reference in their entirety. Exemplary nadicand dinadic endcaps are described in U.S. Patent Application PublicationNo. 2008/0300374 titled Dinadic Phenyl Amine Reactive Endcaps toLubowitz et al.

Polyimide oligomers of the formula: D_(i)-Q-D_(i) may be prepared byreacting the suitable endcap monomers with the monomer reactants thatare commonly used to form the desired backbone. For example, an imide oran imidesulfone is prepared by reacting an endcap monomer with a diamineand a dianhydride in accordance with the method described in U.S. Pat.No. 4,584,364. Ethersulfones can be prepared by reacting an endcapmonomer with a suitable dialcohol (i.e., diol, bisphenol, or dihydricphenol) and a dihalogen as described in U.S. Pat. No. 4,414,269 or othercondensation reactions.

The resin system previously described herein can comprise at least oneof Y_(i)-A-Y_(i) and Z_(i)—B—Z_(i) combined with D_(i)-Q-D_(i). Theresin system can comprise any ratio of the aforementioned polyimideoligomers. As previously discussed the polyimide oligomers may bepre-imidized or formed in-situ. Changing the ratio of the polyimideoligomers typically changes the physical properties in the finalcomposites. Curing the polyimide oligomers involves mutual(interlinking) polymerization and addition polymerization.

The individual polyimide oligomers should initially have relatively lowaverage formula weights and, accordingly, should remain relatively easyto process until curing when the extended chain is formed to produce thecomposite. For nadic and dinadic endcaps curing is typically performedunder pressure to prevent volatilization of cyclopentadiene. Forphenylethynyl and diphenylethynyl endcaps, vacuum processing may beused.

Another aspect of the present disclosure pertains to producinghigh-temperature composites. Resin systems produced in accordance withimplementations of the present disclosure exhibit densities less thanthose of metal counterparts. Accordingly, composites comprisingpolyimide resins having endcapped oligomers with nanomodified backbonesare ideal for replacing metallic structures to reduce weight. Wherehigh-temperature strength also drives the design, a material with higherallowable strength at elevated temperatures, such as compositeimplementations of the present disclosure, will reduce overallstructural weight. Composites manufactured in accordance withimplementations of the present disclosure can be used to replace otherhigh-temperature composites that require a thermal-protection layer.

Composites and prepregs comprising polyimide oligomer compositionsformulated according to implementations of the present disclosure can byprepared by any conventional technique known in the art. For example, incertain implementations the polyimide oligomers exhibit a melt viscositysuch that a composite can be prepared by known liquid-molding techniquessuch as resin-transfer molding and resin film infusion, among others.Depending on the application, the reinforcement materials can include,without limitation, for example, woven, braided, or knit fabrics,continuous or discontinuous fibers (in chopped or whisker form),ceramics, organics, carbon (graphite), or glass.

For example, a composite can be manufactured by impregnating reinforcingmaterials with a pre-imidized composition according to implementationsof the present disclosure and cured anaerobically and under sufficientpressure to prevent the creation of voids. If the polyimide oligomershaving nanomodified backbones are nadic endcapped, curing will initiallyrelease cyclopentadiene. In such cases, the applied pressure duringcuring should be sufficient to prevent volatilization of thecyclopentadiene and thereby cause the cyclopentadiene to react with theresin itself and become incorporated into the backbone. Suitablepressures for composite fabrication range from atmospheric to 1,000 psidepending upon the nature of the polyimide composition. Depending on thespecific polyimide composition to be cured, the resin systems may becured at temperatures known in the art. For example, the resin systemsby be cured by subjecting them to temperatures ranging from about 200degrees Celsius to about 350 degrees Celsius.

While the foregoing is directed to implementations of the presentdisclosure, other and further implementations of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

All mentioned documents are incorporated by reference as if hereinwritten. When introducing elements of the present disclosure orexemplary aspects or implementation(s) thereof, the articles “a,” “an,”“the” and “said” are intended to mean that there are one or more of theelements. The terms “comprising,” “including” and “having” are intendedto be inclusive and mean that there may be additional elements otherthan the listed elements. Although this disclosure has been describedwith respect to specific implementations, the details of theseimplementations are not to be construed as limitations.

1. A resin system, comprising: a first capped oligomer having theformula:Y_(i)-A-Y_(i), wherein: i=1 or 2; Y is a nadic or dinadic functionalendcap; and A is a chemical backbone, wherein the chemical backbonecomprises one or more nanoparticles; and a second capped oligomer havingthe formula:D_(i)-Q-D_(i), wherein: i=1 or 2; D is a nadic or dinadic functionalendcap; and Q is a hydrocarbon backbone.
 2. The resin system of claim 1,wherein: from about 1% to about 25% of the chemical backbones andhydrocarbon backbones have nadic endcaps; and from about 75% to about99% of the chemical backbones and hydrocarbon backbones have dinadicendcaps.
 3. The resin system of claim 1, wherein the one or morenanoparticles are inorganic nanoparticles.
 4. The resin system of claim1, wherein the one or more nanoparticles are organic nanoparticles. 5.The resin system of claim 1, wherein the one or more nanoparticles haveinorganic portions and organic portions.
 6. The resin system of claim 1,wherein the one or more nanoparticles are selected from the groupconsisting of: functionalized silsesquioxanes, functionalized carbonblack, functionalized silicates, functionalized graphene, functionalizednanographite, functionalized carbon nanotubes, functionalized halloysitenanotubes, functionalized boron nitride nanotubes and combinationsthereof.
 7. The resin system of claim 1, wherein the chemical backbonefurther comprises one or more moieties selected from the groupconsisting of: imidesulfone, ether, ethersulfone, amide, imide, ester,estersulfone, etherimide, amideimide, oxazolyl, oxazolyl sulfone,thiazolyl, thiazolyl sulfone, imidazolyl, imidazolyl sulfone,heterocyclyl sulfone, and combinations thereof.
 8. The resin system ofclaim 7, wherein the hydrocarbon backbone includes one or more moietiesselected from the group consisting of: imidesulfone, ether,ethersulfone, amide, imide, ester, estersulfone, etherimide, amideimide,oxazolyl, oxazolyl sulfone, thiazolyl, thiazolyl sulfone, imidazolyl,imidazolyl sulfone, heterocyclyl sulfone, and combinations thereof. 9.The resin system of claim 1, wherein the dinadic functional endcaps aredinadic phenyl amine endcaps selected from the group consisting of:

and combinations thereof, wherein NA is a nadic anhydride.
 10. The resinsystem of claim 9, wherein NA is illustrated by the formula:

wherein G=—CH₂—, —SO₂—, —S—, —O—, or —CO—, and R=hydrogen, lower alkylor phenyl.
 11. The resin system of claim 1, wherein the nadic functionalendcaps are nadic phenyl amine endcaps selected from the groupconsisting of:

and combinations thereof, wherein NA is a nadic anhydride.
 12. The resinsystem of claim 11, wherein NA is illustrated by the formula:

wherein G=—CH₂—, —SO₂—, —S—, —O—, or —CO—, and R=hydrogen, lower alkylor phenyl.
 13. A resin system according to claim 1, wherein at leastpart of the first capped oligomer is reacted with at least part of thesecond capped oligomer to form a reaction product. 14-20. (canceled) 21.The resin system of claim 6, wherein the nanoparticles arefunctionalized with one or more functional groups selected from thegroup consisting of: carboxy, epoxy, ether, ketone, amine, hydroxy,alkoxy, alkyl, aryl, aralkyl, alkaryl, lactone, and combinationsthereof.
 22. The resin system of claim 1, wherein the one or morenanoparticles are covalently attached to Y.
 23. A resin system,comprising: a first capped oligomer having the formula:Y_(i)-A-Y_(i), wherein: i=1 or 2; Y is a nadic or dinadic functionalendcap; and A is a chemical backbone, comprising: one or morenanoparticles selected from the group consisting of: functionalizedsilsesquioxanes, functionalized carbon black, functionalized silicates,functionalized graphene, functionalized nanographite, functionalizedcarbon nanotubes, functionalized halloysite nanotubes, functionalizedboron nitride nanotubes and combinations thereof; and one or moremoieties selected from the group consisting of: imidesulfone, ether,ethersulfone, amide, imide, ester, estersulfone, etherimide, amideimide,oxazolyl, oxazolyl sulfone, thiazolyl, thiazolyl sulfone, imidazolyl,imidazolyl sulfone, heterocyclyl sulfone, and combinations thereof; anda second capped oligomer having the formula:D_(i)-Q-D_(i), wherein: i=1 or 2; D is a nadic or dinadic functionalendcap; and Q is a hydrocarbon backbone.
 24. The resin system of claim23, wherein the dinadic functional endcaps are dinadic phenyl amineendcaps selected from the group consisting of:

and combinations thereof, wherein NA is a nadic anhydride.
 25. The resinsystem of claim 24, wherein NA is illustrated by the formula:

wherein G=—CH₂—, —SO₂—, —S—, —O—, or —CO—, and R=hydrogen, lower alkylor phenyl.
 26. The resin system of claim 23, wherein the nadicfunctional endcaps are nadic phenyl amine endcaps selected from thegroup consisting of:

and combinations thereof, wherein NA is a nadic anhydride.
 27. The resinsystem of claim 26, wherein NA is illustrated by the formula:

wherein G=—CH₂—, —SO₂—, —S—, —O—, or —CO—, and R=hydrogen, lower alkylor phenyl.